The present invention relates to a machine tool, especially a hammer drill or chisel hammer or chipping hammer, and, more particularly, to a machine tool having a rotatably driven and/or hammering tool holder for receiving a tool with a grooved shaft, which has a base body with at least one radially movable locking body, which engages in a closed groove in one end of a shaft of a tool held in the tool holder and which is retained in a locking position by a releasable bearing member, which may be moved into a releasing position in which the locking body is radially released so that it can move into its unlocking position by means of an operating element.
A hammer drill machine with a rotatably driven tool holder is disclosed in EP 0 456 003 B1. The tool holder has a base body and a receptacle arranged in it for a drill or a hammer tool, in which a chuck with jaws acting as a first tool-holding means and a special second tool-holding means for a tool provided with a grooved shaft are arranged. The special second tool receptacle has a radially slidable locking element in the form of a locking ball, which is movable into a closed groove on a shaft end of the tool and which is held in its locking position by a retaining or bearing sleeve and a locking sleeve having limited axial movability. The locking sleeve is spring-loaded so as to be urged over the retaining sleeve in the direction of its holding position. In the locking position of the locking ball the locking sleeve radially overlaps the locking ball and the retaining sleeve locks the locking ball with an axially projecting portion.
When the tool is inserted the locking ball is pushed into a longitudinal slot in the insertion direction by the shaft end of the tool. Thus the projecting portion of the retaining sleeve is pushed against the spring by means of the locking ball. A free space, in which the locking ball can escape radially to the outside, arises between the locking sleeve and the retaining sleeve. The tool can be inserted. Subsequently the pre-compressed spring slides the locking sleeve into its initial position and presses the locking ball in the grove of the tool.
To take the tool out of the tool holder the locking sleeve is pushed against the retaining sleeve with an operating element and against the spring loading the retaining sleeve, so that the locking ball can radially escape to the outside and the tool can be removed. After that the spring forces the retaining sleeve, the locking sleeve and the locking ball back into their initial position.
It is an object of the present invention to provide an improved machine tool.
This object, and others which will be made more apparent hereinafter, are attained in a machine tool having a rotatably driven and/or axially movable tool holder for receiving a tool with a grooved shaft, which comprises a base body with at least one radially movable locking body, which engages in at least one closed groove in one end of a shaft of a tool held in the tool holder and which is retained in a respective locking position by a releasable bearing member, which may be moved into a releasing position, in which the locking member is radially released, by means of an operating member.
According to the invention the tool holder has a guiding member arranged to guide the at least one locking body radially outward during motion from the locking to the unlocking position when the releasable bearing member is in the releasing position. The guiding member acts on the at least one locking body under a radially inwardly directed spring force. Tipping and tilting of the at least one locking body is thus prevented by the guiding spring force and axial motion of the at least one locking body is not required.
In preferred embodiments of the invention the radially inwardly directed spring force can be produced by one or more separate spring elements acting on the guiding member. Advantageously in a particularly preferred embodiment the guiding member or structural element is elastically deformable or resilient. The required spring force can then be produced at least partially, preferably completely, by the guiding member itself. These preferred embodiments have a reduced number of components, take up less space and have reduced assembly costs in comparison to other embodiments.
The guiding member can comprise any of a number of different elastic materials, which appear to be significant to one skilled in the art. These elastic materials include metal and plastic. The plastic guiding members, however, are particularly light and economical.
Furthermore the guiding member can have a variety of different shapes. For example, it can be ring-shaped, bar-shaped, etc, and can be compressible rubber packing, an elastic rubber or plastic bar, etc. If the guiding member is in the form of a sleeve, it can be easily assembled because of its rotational symmetry. Assembly errors can thus be avoided.
In order to save space and additional components, the operating member is guided in its motion by means of the guiding member and/or the guiding member is made in one piece with the operating member.
The locking bodies can have different shapes. For example, they can be square, spherical or take some other shape that appears significant to one skilled in the art. However if the locking body is shaped like a roll or roller, economical standardized parts result. Rolls or rollers have large transmission surfaces in their rotation directions. Torque transmission elements can be replaced or at least advantageously assisted by the rolls or rollers.
In a particularly preferred embodiment of the invention at least one portion of the tool holder is mounted axially slidable for producing an idle connection or drive connection and the locking body has a length substantially equal to that of the groove in the tool. By guiding the locking body by means of the spring force the locking body advantageously can be guided radially to the outside without axial motion. The locking body can have the maximum length and a maximum torque transmission can be obtained from this locking body. Large transmission surfaces in the rotation direction, small surface pressing values, smaller wear and longer service life can be attained for the locking body and the torque transmission elements.